Conventionally, a seal ring that seals the annular gap between a shaft and a housing rotating relative to each other has been used in an Automatic Transmission (AT) or a Continuously Variable Transmission (CVT) for an automobile to maintain hydraulic pressure. In order to improve the fuel efficiency of an automobile or reduce the wear-out of a seal ring, it is preferable that the rotational torque of the seal ring be low. In view of this, there has been conventionally known technology for providing a groove into which sealed fluid is introduced, on the lateral surface of a seal ring that serves as a sliding surface at the time of its relative sliding (see PTL 1). In a seal ring disclosed in PTL 1, a flow path (groove) into which sealed fluid is introduced from the side of the inner periphery of the seal ring is formed over a circumference on the side of the inner periphery of the sliding surface (lateral surface) of the seal ring. When the sealed fluid is introduced into the flow path, the surface pressure of the sliding surface reduces with the generation of dynamic pressure. Therefore, the rotational torque (frictional torque) of the seal ring is reduced.